Hardened-plaster product



Patented n... 4, 1928.

' UNITED STATES PATENT OFFICE. v

WILLIAI HOFI'IAN 30m, 01' NEW YORK, N. Y., SIG-N03 TO TEXAS GULF BUL-rnun columnar, or BAY crrY, TEXAS, a oonrom'rron or rnxas.

, EARDENED-PLASTER PRODUCT.

Io Drawing.-

This invention relates to articles or products made of hardenedplaster,and has for its object the provision of certain improvements in themanufacture of such articles or 6 products, as well as the provison ofan improved article or product of this character. Various articles andproducts of commerce are made up in whole or in part of hardened laster;plaster board being perhaps the best own example of such products. Theordinary plaster boards of commerce are made up of a body of hardenedplaster, usually gypsum plaster, covered in whole or in art with fibrousmaterial. In my co-pen ing atent application, Serial No. 175,432, filedarch 14, 1927, I have disclosed certain im provements in plaster boardmanufacture involving genera ly the impre nation with sulfur of thefibrous covering for the hardened plaster body as well as thestrengthening of the bond between the "fibrous covering and the plasterbody by congealed sulfur. These improvements, however, did notcontemplate the impregnation with sulfur of the hardened I l as plasterbod yilother than a slight surface penetration. e present'invention isdirected towards the impregnation with sulfur of the hardened plasterbody itself, and involvesa new method of impregnating gypsum plaster andthe like with sulfur. While the in-' vention is primarily directedtowards plaster board roducts, such as Rock Lath, Sheet Rock, yp Lap,Sackett Board et al., it is ap-' plicable to hardened plaster productsin general,1with or without coverings of fibrous materia The body orinterior of plaster board is ordinarily hardened gypsum plaster. Bygypsum 1 mean calcium sulfate, with or without water of crystallization,plasterof Paris,

anhydrite, alabaster and all natural and commercial forms of thesesubstances. Gypsum usuall occurs with two molecules of water of zrystalization (CaSO,.2H O) and is calcined until the wate'r ofcrystallization is reduced to one-half molecule -CaSO,-.1/2H,O) or untilall of the water 0 crystallization has been driven off. After calciningand grinding the gypsum is mixed with water which causes it to set orharden. Although the'exact chemical changes which take place areobscure, it is proba le that the gypsum reverts to its native or initialstate with two molecules of in excessive cracking and disintegration-Application filed 1mm 14,1927. Serial r. 115,421.

water of crystallization. However this may be, so far as thepresentinvention is concerned it is applicable to all forms of set or hardenedgypsum plaster regardless of the water content. s Ordinary set orhardened gypsum or similar laster containing materialsv such as'plasteroard, cannot be satisfactorily impregnated with molten sulfur byimmersion in a bath of this substance probably, on account of thecombined water in the gypsum. Long eriods of immersion, evenup totwenty-four ours or more, frequently have no effectexceptingtoimpregnate the immediate surface or for a slight depth of a quarter ofan inch or less, and the resulting product. is very frangible andinvariablycracked. It appears that the sulfur will not 'enter ordinarygypsum or gypsum "containing materials even though the temperature ofthe molten sulfur bath is suchasto partiallydrive off the comb nedwater. It appears that driving out 7! the coinbinedwater in this way hassome deleterious effect on the gypsum, probably due to the rapidity ofdrivingrofi water or calcination which notonly retards or entirelyprevents the entry of the sulfur, but results so I have discovered thatby slowly preheat mgthe set or hardened gypsum or plaster containingarticles, that they may be very. successfully and satisfactorilyimpregnated 35 or treated by immersion in a bath of molten sulfur at 120to 160 0., or even higher temperatures may be used where paper, fibrousor similar organic products are not. involved. It appears essential, notto merely dry the set or hardened gy sum or similar plaster containingmateria so as to drive ofl absorbed water, but toactually heat thearticles to a degree to substantially drive off the combined Water and Iprefer to employ a temperature at least equal to or higher than thetemperature of the saturating bath to be subsequently used.

I have further discovered that it is more important to preheat and driveoff the combined moisture existing in set or hardened gypsum block andpure set or hardened gypsum products than in'the case of set or hardenedgypsum combined with fibrous materials or covered with fibreboard orpaper such as Sheet Rock, but this may be-due to the fact that \thesecoverings partially mitigate or prevent the cracking or disinte ationpreviousl described. It is advisab e, however, to pre eat all of theseproducts that contain set or hardened gypsum although in the case ofthose containing paper or organic fibrous materials, the heat can notbecarried to such a point that it would tend to char the fibres.

In the case of Sheet Rock or similarfibrous gypsum articles,

containing set or hardened I. have found that they may e safely heatedto approximately140 C. while straight set or hardened gypsum bloclrpractically any reasonable degree of temperature and I have carried itas igh as 250 C. at which int the gypsum is completely or substanti ycalcined.

It is important, however, to preheat the set or hardened sum or similargypsum prod not at least as igh or higher than the temperature of thesulfur bath in which it is to be subsequently treated, either with orwithout vacuum and pressure. This apparently prevents any moisture orcombined water being driven out'by the heated sulfur of the sulfurimpregnating-bath, which I have found is the cause of the disintegrationand crack ing and also which is responsible for the pregree ofimpregnation has resulted. It is dis ventin of the-ent of the sulfur.

sheets of rock lath or similar set or hardened gypsum containingarticles, are immersed 1n I a bath of molten sulfur either in.horizontal or vertical position at a temperature not in excess of thepreheating temperature and allowed to remain therein untilthe desireddetinctly understood that this method is not limited to completeimpregnation because in many cases I prefer to simply treat or imre atethe immediate surface of the set or Ear ened psum or the exposed fibrousmaterials an the contiguous set or hardened psum. .The im regnation ofthe exposed fibrous materials ollowing preheating may be accomplished inthirty minutes to one hour or less, depending upon the thickness of thefibre covering Upon remove. from the treatin bath the molten sulfur-isheld within the fi re covering and in the set or hardened psum.immediately adjacent thereto b capi larity and this sulfur, due to itslow atent heat very quickly solidifies especially if placed in a currentof air or otherwise chilled and the loss from exudation or dri ping isnegligible.

These-sulfur treat fibre-gypsum articles if not perfectly flat may be.ressed while still hot or after the first solidi cation of the sulfurand while it is in its monoclinic stage .and more or less dplastic, andin this way a perfectly true an flat product assured. As a rule,however, the productsmentioned are may be heated to parts for generallyflat and this is unnecessary. On,

the other hand, thgy may be deliberately curved or otherwise aped to aslight degree if this IS desirable, but it is important to manipulatethem while the sulfur is either molten or in its transition stage as oneof the great advanta es of the treatment is the fixation which is roughtabout by stable, rhombic crystals of sul ur.

In my co-pending patent applications Serial No. 61,831, filed October10, 1925 and Serial No. 124,784 filed July 24, 1926, methods aredescribed for coloring sulfur and for coloring various materials withcolored sulfur, and I find that the processes there described areapplicable in the practice of the present invention. In accordance withthe methods there described I may include in the practice of the presentinvention, sulfur soluble dyes .with the sulfur and thereby attractiveshades .of color to these various gypsum products and I find that thecolor penetrates as far as the sulfur itself and is of a highlypermanent nature.

Products made in accordance with the invention have numerous practicalcommercial advantages. 'Set gypsum, in itself, or the various objectscomposed in part of set upsum is' not proof against weather or moistureand consequently cannot be used out of doors. These products arehydroscopic and rapidly disintegrate when exposed to moisture and. arereadily acted upon by various acids and chemical fumes. They also lackphysical strength for many pur oses.

I have discovered t at articles composed wholly or in part of set orhardened gypsum when treated in accordance with the method of theinvention, are proof against all normal weather. conditions andsatisfactorily withstand the various acids and chemical fumes. Theincrease in strength under tension, compression and cross-bending,amounts to three or four fold and sometimes more, depending to somedegree upon the extent of the penetration of the sulfur into thegypsumitself.

The new set or hardened gypsum product ofthe invention ma be painted,varnished, lac .ueredor shellac ed and will take ractica ly any finishor it may be colored as erein order to reduce inflammability, it is.desirable to give the. im regnated article a fim ishing coat of paint oracquer. These highly finished materials are suited for various purposes, such for instance as radio panels, wall roducts, such as.

tile and various sanitary artitions, base ards,- and. as a general anstitute'for slate and other materials.

While I have mentioned various commercial forms of set psum orplasterboard, I

do not wish to con e myself entirely to these products, since theinvention is not limited terial impregnated either wholly or in part tothe use of these particular products, but is with sulfur. applicable toany form of hardened plaster 3. An article of manufacture comprising 15or set gypsum. The hardened plaster or set dehydrated set gypsumimpregnated either 6 gypsum may contain .or be associated with wholly orin part with colored sulfur.

some for-in of fibrous material. 4.1 An artic e of manufacturecomprising I claim: dehydrated set gypsum and a fibrous material l.-Anarticle of manufacture comprising impregnated either wholly or in partwith -20 dehydrated set gypsumimpregnated either colored sulfur. I ywholly or in part with sulfur. v In testimony whereof I afiix mysignature.

2. An article of manufacture comprising dehydrated sot gypsum and afibrous ma- WILLIAM HOFFMAN KOBBE.

